The narrative contrasts the demeanor, outlook, purity, and power of the converts with the ugliness of those who had not been converted.
The book of Alma teaches more about the repentance process: through the merits of God’s Son (that is, through his justice, mercy, compassion, love, and infinite sacrifice), we can be forgiven of all our sins—little ones and big ones. This includes having the guilt taken away from our hearts—not the memory (that stays as an early-warning system to help us keep our distance from those sins), but the guilt and stain can be totally removed.
Another pivotal concept in the cleansing of sins is “to get God to take them away from our hearts.” The disposition or desire to sin can be taken away by the Savior if we ask him to do so. Bad thoughts or desires to do wrong that come into our minds or hearts may be displaced and removed by God himself if we ask him to do so. We can also help by constantly filling our minds with uplifting thoughts, good music, and memorized scriptures.